1. Field of the Invention
Aspects of the present invention relate to a method and apparatus to optimize a writing condition for an optical recording medium, and an optical recording medium therefore.
2. Description of the Related Art
A conventional writing condition optimizing method may include determining a write pulse having a minimum phase difference by extracting a phase difference between a writing pattern edge and a PLL (phase lock loop) clock edge as an error pulse during reproduction after writing is performed in a predetermined pattern, obtaining a condition in which the error pulse from an information table is minimized where the phase difference exists, according to a combination of a mark and a space, and repeating an operation of writing and reproducing a writing pattern with respect to a disk.
Another conventional writing condition optimizing method includes a method of optimizing writing by minimizing jitter. In this method, writing power is first optimized in an asymmetry correction method. Then, a writing pulse is determined by shifting a mark edge. That is, the first pulse and last pulse of the writing pulse is determined to minimize a jitter value.
These methods basically measure jitter using a zero-crossing method or optimize writing using the phase difference between the writing pattern edge and the PLL clock edge. However, as capacities of disks increase, use of the above and/or other methods become impossible.
FIGS. 1A and 1B are graphs respectively showing 25 GB and 50 GB RF signals measured using a pickup having a wavelength of 405 nm and NA of 0.85 in which a resolution is 119 nm (=405 nm/(4×0.85)). As shown in FIG. 1, for a 25 GB RF signal, the RF signal is clear so that the signal can be evaluated in the zero-crossing method and so that writing optimization is possible using the method. That is, since the RF signal is clearly crossing a zero point, as indicated by a circle A, the writing optimization is possible in the zero-crossing method.
As shown in FIG. 1B, for a 50 GB RF signal, since a signal less than a resolution (2 T=75 nm and 3 T=112.5 nm) cannot be detected, writing optimization cannot be achieved in the above-described conventional writing condition optimizing method. That is, since the RF signal does not cross the zero point in a portion indicated by a circle B, detection of the zero crossing of a writing RF signal is difficult.
This phenomenon is the same in a random signal of a Super-RENS disk including marks that are smaller than a resolution. In the Super-RENS disk, the size of a laser beam itself is not decreased but an optical characteristic changes in a partial area of the disk. Thus, since the length of a mark is decreased while the original size of the laser beam is unchanged, marks are positioned within a range of one spot of a laser beam and, thus, interfere with a signal. When the signal level of a particular mark is influenced by the signal levels of marks located before and after the particular mark due to the above-described inter-symbolic interference, the signal level of a mark or space becomes inconsistent even when the length of the mark or space is identical. Accordingly, the zero-crossing method cannot be used. Therefore, the writing optimizing method used for the conventional optical disk cannot be used for a Super-RENS disk, which includes marks smaller than a resolution. Thus, a new method is needed for the writing optimization.